What is the best explanation from the nurse as to why a client must return to the unit in 48 hours after having a tuberculin skin test intradermal?

A tuberculin skin test is done to see if the patient has ever been exposed to the bacteria that causes tuberculosis (Mycobacterium tuberculosis). The test is done by putting a small amount of antigens of the bacteria under the skin.

If the patient was exposed, there will be a firm red bump where the antigens were placed but it would take 2 days to see the results so the patient needs to come back again after that time.